"He's going to be a little bit behind on games," Melvin said. "We weren't really sure how he would respond here. Straight-ahead [running] is fine with him, but the issue he's having is slowing down, and he gets going pretty fast."

Considering just how much Mateo relies on his speed, which is perhaps his biggest attribute, the A's plan to be extra cautious with the 22-year-old, who is ranked by MLB Pipeline as the organization's No. 4 prospect behind Franklin Barreto, A.J. Puk and Dustin Fowler.

Mateo has 234 stolen bases in 452 Minor League games.

"He feels pretty good, and we're probably holding him back some," Melvin said. "At this time of spring, we're going to be conservative, especially with a guy like him."

The A's have long been lacking athleticism in their system, which is why they've been so anxious to see Fowler and Mateo -- products of the Sonny Gray deal -- this spring. Fowler, too, is slightly behind schedule as he continues rehabbing from right knee surgery, but he's expected to be in games by the end of the month.

While Fowler is being groomed for the A's everyday job in center field, Mateo is expected to begin the season at Triple-A Nashville. Melvin, however, planned to give him a long look this spring.

"I wanted to get him a lot of at-bats here early in spring," Mevlin said. "We've been talking about our athleticism, and Fowler and Mateo are two key guys. So to not have a guy that we were going to look at extensively -- and maybe our most athletic guy -- [is] a little disappointing, but we obviously have to be careful with him."

Melvin plans to keep Mateo at shortstop this spring, despite ongoing conversations about having him clock time in center field as well.

"We talked about maybe some center, but at this point we're just going to try to get him into some games," Melvin said. "I know he just wants to be out in the field, whether it's second, whether it's short, or the outfield. We discussed the dynamic of the outfield but at this point probably just getting ahead of ourselves. We just want him healthy and back on the field and concentrate on the middle of the field."